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Diffstat (limited to '')
| -rw-r--r-- | src/shared/nscd-flush.c | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/src/shared/nscd-flush.c b/src/shared/nscd-flush.c new file mode 100644 index 0000000..6df18d7 --- /dev/null +++ b/src/shared/nscd-flush.c @@ -0,0 +1,142 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <fcntl.h> +#include <poll.h> + +#include "fd-util.h" +#include "io-util.h" +#include "nscd-flush.h" +#include "socket-util.h" +#include "strv.h" +#include "time-util.h" + +#define NSCD_FLUSH_CACHE_TIMEOUT_USEC (5*USEC_PER_SEC) + +struct nscdInvalidateRequest { + int32_t version; + int32_t type; /* in glibc this is an enum. We don't replicate this here 1:1. Also, wtf, how unportable is that + * even? */ + int32_t key_len; + char dbname[]; +}; + +static int nscd_flush_cache_one(const char *database, usec_t end) { + size_t req_size, has_written = 0, has_read = 0, l; + struct nscdInvalidateRequest *req; + _cleanup_close_ int fd = -EBADF; + int32_t resp; + int events, r; + + assert(database); + + l = strlen(database); + req_size = offsetof(struct nscdInvalidateRequest, dbname) + l + 1; + + req = alloca_safe(req_size); + *req = (struct nscdInvalidateRequest) { + .version = 2, + .type = 10, + .key_len = l + 1, + }; + + strcpy(req->dbname, database); + + fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0); + if (fd < 0) + return log_debug_errno(errno, "Failed to allocate nscd socket: %m"); + + /* Note: connect() returns EINPROGRESS if O_NONBLOCK is set and establishing a connection takes time. The + * kernel lets us know this way that the connection is now being established, and we should watch with poll() + * to learn when it is fully established. That said, AF_UNIX on Linux never triggers this IRL (connect() is + * always instant on AF_UNIX), hence handling this is mostly just an exercise in defensive, protocol-agnostic + * programming. + * + * connect() returns EAGAIN if the socket's backlog limit has been reached. When we see this we give up right + * away, after all this entire function here is written in a defensive style so that a non-responding nscd + * doesn't stall us for good. (Even if we wanted to handle this better: the Linux kernel doesn't really have a + * nice way to connect() to a server synchronously with a time limit that would also cover dealing with the + * backlog limit. After all SO_RCVTIMEO and SR_SNDTIMEO don't apply to connect(), and alarm() is frickin' ugly + * and not really reasonably usable from threads-aware code.) */ + r = connect_unix_path(fd, AT_FDCWD, "/run/nscd/socket"); + if (r < 0) { + if (r == -EAGAIN) + return log_debug_errno(r, "nscd is overloaded (backlog limit reached) and refuses to take further connections: %m"); + if (r != -EINPROGRESS) + return log_debug_errno(r, "Failed to connect to nscd socket: %m"); + + /* Continue in case of EINPROGRESS, but don't bother with send() or recv() until being notified that + * establishing the connection is complete. */ + events = 0; + } else + events = POLLIN|POLLOUT; /* Let's assume initially that we can write and read to the fd, to suppress + * one poll() invocation */ + for (;;) { + usec_t p; + + if (events & POLLOUT) { + ssize_t m; + + assert(has_written < req_size); + + m = send(fd, (uint8_t*) req + has_written, req_size - has_written, MSG_NOSIGNAL); + if (m < 0) { + if (errno != EAGAIN) /* Note that EAGAIN is returned by the kernel whenever it can't + * take the data right now, and that includes if the connect() is + * asynchronous and we saw EINPROGRESS on it, and it hasn't + * completed yet. */ + return log_debug_errno(errno, "Failed to write to nscd socket: %m"); + } else + has_written += m; + } + + if (events & (POLLIN|POLLERR|POLLHUP)) { + ssize_t m; + + if (has_read >= sizeof(resp)) + return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Response from nscd longer than expected: %m"); + + m = recv(fd, (uint8_t*) &resp + has_read, sizeof(resp) - has_read, 0); + if (m < 0) { + if (errno != EAGAIN) + return log_debug_errno(errno, "Failed to read from nscd socket: %m"); + } else if (m == 0) { /* EOF */ + if (has_read == 0 && has_written >= req_size) /* Older nscd immediately terminated the + * connection, accept that as OK */ + return 1; + + return log_debug_errno(SYNTHETIC_ERRNO(EIO), "nscd prematurely ended connection."); + } else + has_read += m; + } + + if (has_written >= req_size && has_read >= sizeof(resp)) { /* done? */ + if (resp < 0) + return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "nscd sent us a negative error number: %i", resp); + if (resp > 0) + return log_debug_errno(resp, "nscd return failure code on invalidating '%s'.", database); + return 1; + } + + p = now(CLOCK_MONOTONIC); + if (p >= end) + return -ETIMEDOUT; + + events = fd_wait_for_event(fd, POLLIN | (has_written < req_size ? POLLOUT : 0), end - p); + if (events < 0) + return events; + } +} + +int nscd_flush_cache(char **databases) { + int r = 0; + + /* Tries to invalidate the specified database in nscd. We do this carefully, with a 5s timeout, + * so that we don't block indefinitely on another service. */ + + usec_t end = usec_add(now(CLOCK_MONOTONIC), NSCD_FLUSH_CACHE_TIMEOUT_USEC); + + STRV_FOREACH(i, databases) + RET_GATHER(r, nscd_flush_cache_one(*i, end)); + + return r; +} |